|At Takadanobaba station (src).|
First of all, do not be afraid of asking people for help. Even though most don't speak fluent or much English they are normally very polite, and will try to help you as best they can.
Nowadays you don't need anything but data traffic on your mobile. Order a "data traffic only" SIM card from eConnect Japan. Do this before you travel, and have it waiting for you at the post office at the airport (the post office at Narita is located at the forth floor, inside the airport shopping mall).
Do you have a lot to carry? Let someone else do the job! There are baggage deliver services at the airport. Drop of your heavy bags with them, and let them drive them to your place in the city. It's cheap and super convenient (I used GPA, and was very satisfied).
Plan Your Commute
Google Maps is brilliant for finding the best way to get from A to B, or for example from the airport to your hotel. The trains are fast, and on time. Use them instead of considering a taxi, which quickly will become very expensive.
As you will frequently use the trains in Tokyo, you should get a PASMO card to pay for your travel. With it you don't have to figure out the price from one place to another. And don't worry, you can refill the card as you are about to leave a station, next to when you enter.
Make sure you have plenty of cash. Japan is a land where you use a lot of cash. It is also not that easy to find ATMs where you can withdraw cash, using for example a VISA card. Post offices and Citibank for the rescue!